The present invention relates to a system for transmitting power of an engine to driving wheels of a motor vehicle, and more particularly to a trans-axle type automatic transmission, an input shaft of which extends across an axle of the vehicle.
A trans-axle type automatic transmission has a torque converter for transmitting the power of an engine, an automatic transmission device having an input shaft operatively connected to the torque converter, a drive pinion shaft disposed in parallel with the input shaft, and a drive pinion formed on an end of the drive pinion shaft being engaged with a ring gear of a differential provided in an axle system. Vertical, longitudinal and lateral dimensions of the automatic transmission must be determined with consideration to structure and form of the vehicle, effect on braking operation of the vehicle, reliability, and oscillation of the axle system, noise and driveability. For example, it is necessary to minimize the horizontal distance between the front end of the engine and the axle shaft connected to the differential in order to reduce the minimum turning outer radius. Lateral and vertical relative positions of the centers of the differential and tires are also significant a regarding braking effect and strength and durability of the axle shaft. The longitudinal distance from the front end of the engine to the axle shaft, and the vertical distance between the axle shaft and the top of the engine are preferably reduced to provide a slant-nosed form of the body of the vehicle, ensuring improved aerodymanic characteristics. Additionally the vertical distance between the crankshaft and a bottom of a housing of the automatic transmission device must also be minimized for better ground clearance, resulting in improvement in driveability.
One of the conventional arrangements of the trans-axle type transmission is disclosed in Japanese Patent Publication 58-24289. In the arrangement, the crankshaft and the drive pinion shaft of the differential are disposed in parallel with each other so that axial centers thereof are positioned in a vertical plane. In order to reduce the above described dimensions, the differential is deviated to one side from the longitudinal center line of the vehicle. Accordingly, lengths and hence angles at universal joints of the right and left axle are not equal to each other, causing oscillation of the steering wheel, deviation from a course and an unbalanced braking effect. In order to prevent these troubles, a damper is provided on the longer axle shaft.
However, provision of the damper not only results in increase in the number of parts and cost, but requires a difficult fine tuning operation and hence unpreferable for maintenance of the axle system. But if the differential is disposed at a central position with respect to the width of the vehicle, the vertical distance between the differential and the input shaft increases. This is because since the axis of the drive pinion shaft must be in parallel to that of the crankshaft to maintain a certain distance between the drive pinion shaft and components of the automatic transmission device, the center of the drive pinion shaft must be on an arc having the axis of the crankshaft as the center.